This invention relates to paper webs and more particularly for a method and apparatus for decurling paper or paper board webs prior to the webs being utilized in some other downstream process.
In the process of making paper (cardboard or a similar product is in this application also considered defined as xe2x80x9cpaperxe2x80x9d) on a papermachine and/or coating paper forces and temperature gradients within the paper can cause it to curl to one side or the other of the web. Curl is normally the result of stresses unequally applied to the paper, say as by winding a web of paper into a roll, causing strains which become set into the rolled paper and when released, as when the roll is unwound, can cause a web or the subsequently cut sheet to curl. For example, running the web over dryer xe2x80x9ccansxe2x80x9d (rolls), causes the paper to take on the curve of the roll; wetting one side of a web as is done during applying coating to one side can also induce a curl, in a subsequently dried web. Even more frequent is the tendency to induce curl when winding a web onto a roll core when the paper is produced. Then there is a xe2x80x9croll setxe2x80x9d curl when the roll is unwound and cut into sheets. While curl is less undesirable in some operations, where the web remains intact, curl is of a greater concern if the web is to be subsequently cut into sheets. Many of today""s subsequent paper converting operations, such as forming sheets from a web, and the use of these sheets, as in printing presses and numerous office products, like photocopy machines, facsimile machines and office printers, are sensitive to curl. With too much curl, the cut or formed sheet of paper will have difficulty feeding properly in such uses. It is therefore desirable to limit or eliminate curl while the paper is in web form, before it is subsequently cut into sheets. Various attempts in the past have been made to limit or eliminate curl.
It is conventional to employ web decurlers in various paper converting operations, such as in a sheeter (a machine that converts a roll into cut sheets). These prior art decurlers were usually configured to provide a decurling action by running the web of paper over a small radius decurler, such as a small diameter roll or a non-rotating stationary bar with its edge machined into a small radius. The web is usually carried on the upstream and downstream side of the decurler bar or roll by rotating, cylindrical web supporting rolls. The amount of decurling affected is partly determined by the depth the web is deflected from its initial position on the web support rolls and/or wrap angle of the web around the decurling radius. In this respect the decurler bar or roll operates in a similar manner as a table edge, wherein a tensioned sheet of paper is drawn across the table edge to remove or induce curl. While it is clear why curl would be removed on a sheet, sometimes it is helpful to induce a curl to solve runability problems. The conventional, prior art decurler is effective if the web has an even xe2x80x9ccross directional curl,xe2x80x9d that is the curl is uniform in a direction running across the web. This type curl is referred to as an xe2x80x9cevenxe2x80x9d cross directional curl profile. That is, the tendency of the paper to curl is uniform across the width of the web. However, some webs have curl profiles that can be asymmetrical or non-uniform. Such non-uniform curl can be caused by various factors such as web caliper differences which need not be addressed here. When the web has less than ideal cross direction curl profile, an uneven decurling effect can be created across the width of the web because of unequal tension of the web when traveling around the radius of the decurler bar or roll. An uneven cross directional curl profile can cause one side of the web, its center or combinations of both to receive more or less decurling effect than the rest of the web. This effect is dependent of course on the location of the tight and/or loose areas of the web. Typically, one side of the web may be xe2x80x9cbaggyxe2x80x9d or the center of the web may be xe2x80x9cbaggyxe2x80x9d with the edges tight. The net result is that the prior art, conventional decurlers could not readily evenly decurl webs which initially had uneven curl profiles.
The present invention provides a method and apparatus for decurling a web with both an even and, particularly an uneven, cross directional curl profile.
The decurling method and apparatus of the present invention comprises the steps of leading a paper web which may contain a precurl, say as due to being wound onto a roll core, onto a bowed roll (also sometimes called a xe2x80x9cMount Hopexe2x80x9d roll), the web being wrapped around a portion of the periphery of the bowed roll. As is conventional, the bowed roll has a xe2x80x9cbowxe2x80x9d or high point on one side (the convex side) and a low point on the opposite side (the concave side). Operating the bowed roll, depending on the amount and direction of the bow, can cause a spreading or cross tensioning effect on the web to remove baggyness when decurling from the paper web. This spreading effect is determined by the bow roll setting, that is, where the high of the bow of the bowed roll is aimed in relation to the web, the degree of bow, and wrap angle of the web on that roll. With the high point of the bow set in a direction perpendicular (90xc2x0) to a line that bisects the wrap angle of the web on the bowed roll, a normal operating position is determined. With the bowed roll so set, it causes an even spreading or cross tensioning effect. If that angle is changed so that it is acute (less than 90xc2x0), the center of the web is tightened. If the angle is changed so that it is obtuse (greater than 90xc2x0), the edges of the web are tightened. The spreading effect produced by adjusting the amount of the bow of the bowed roll, alone, may cross tension the web enough so the web distortion (say baggyness) produced by a less than ideal web cross direction profile will be pulled tight for decurling. As noted, the bowed roll mounting has the ability to aim or rotate the direction of the bow so that it is more or less than 90 degrees to the line that bisects the web wrap angle around the bowed roll. When this angle is less than perpendicular, the web will be tightened up in the center. Likewise, if the angle is more than perpendicular the web will be tightened up on both edges. The amount that the bow has to be aimed or rotated is dependent on the amount of the web distortion for which to be compensated and the magnitude of the bow in the bowed roll. The degree of bow in the bowed roll can be varied and/or adjusted, this adjustment being conventional in the bowed roll""s construction.
The decurling method and apparatus of the present invention includes a decurler assembly which may include either a stationary radiused bar or edge or a small diameter, rotating roll. The decurler bar or roll is located adjacent and, preferably, closely downstream of the bowed roll. The web can be displaced, with the decurler (be it a radiused bar or small diameter rotating roll) to load the web in a direction opposite of the precurl, a sufficient distance to remove most, if not all, of the precurl. In addition to their other functions, the first roll in front of (upstream) and behind (downstream) of the decurler act as support rolls to support the web for the decurling operation. In the preferred method, a lead in roll is also provided, and the web is first lead onto the lead in roll and then over the bowed roll. The lead in roll, the bowed roll, the aim of bow, and the motion of the decurler are controlled so that as the decurler is engaged further into the web, the wrap of the web around the bowed roll is kept essentially constant, both in wrap angle and relative aim of the bow to web.
The method and apparatus of the present invention also includes a lead out roll onto which the web is lead from the decurler. Unlike the prior lead out rolls, that of the present invention is not fixedly mounted, but is mounted so that its relative position with respect to the decurler can be changed. Optimally, additional decurling control may be provided by inclining or skewing the lead out roll up or down or to one side or the other of the web to further load one or the other side and its adjacent edge of the web as needed. If desired, or instead, the bowed roll could be constructed to be skewable or inclinable to the web to address a general side to side uneven web curl profile. In the present invention, the bowed roll and lead out rolls can act as the support rolls for the decurler bar or roll and support the web for the decurling operation or step.
In the decurler apparatus and method of the present invention, for decurling a paper web the upstream bowed roll and decurler work substantially independently, but yet in conjunction with one another. Preferably, the bowed roll and decurler bar are mounted on a decurler carriage so that each is independently adjustable without effecting the operation of the other. Thus, the personnel or operator can make proper adjustments of each more readily. In the preferred form, the bowed roll is mounted and powered so that the position of the high point or xe2x80x9cbowxe2x80x9d in the roll can be radially aimed or changed to say xc2x190xc2x0 from its normal, neutral position to change the aim of the bow relative to the web, as desired, to eliminate or limit baggyness in the web prior to decurling. That is, the best position for the bow of the bowed roll is selected to set up the web by reducing or removing baggyness during the decurling operation to permit the downstream decurler bar or roll to work better. Preferably, the bowed roll is adjusted to eliminate or reduce the baggy portion of the web before it reaches the decurler bar or roll. After decurling, some or all of the baggyness may reappear. The decurler bar or roll is mounted so that it can be driven a desired distance into the web in a direction to counteract the initial curl or precurl to eliminate or limit any final curl. Preferably, the decurler bar or roll moves or pivots some distance from but generally about the axle or axis of the bowed row.
As noted, the decurler assembly also may preferably comprise an upstream lead in roll. The lead in roll also is movably mounted with respect to the bowed roll, and preferably spaced some distance from and mounted to move generally about the axle or axis of the bowed roll. This mounting of the lead in roll can keep a generally consistent wrap of the web on the bowed roll in relation to the direction of the bow in the bowed roll, even if the decurler bar or roll is moved into or away from the web to increase or decrease the amount of decurling action. For simplicity, the decurler bar or roll and lead in roll may be spaced apart on opposite sides of the bowed roll and each mounted on a pair of pivoting but connected carriage plates or arms, which are, in turn, mounted on the frame so both the lead in roll and decurler bar or roll pivot together (rotating) about the bowed roll axle, axis or center line. In normal operation, where the decurler bar or roll may engage the web at an ever increasing amount as the unwinding paper roll decreases in diameter to compensate for additional precurl, the web wrap around the bowed roll can be consistently maintained because the upstream lead in roll is rotating generally about the same point on the decurler support frame. Also, the bow may be kept in a desired selected relationship to the web because the axle of the bowed roll and its adjustment for aiming the bow in the desired direction also rotates with the rest of the decurler as mentioned. In this way, engaging or principally disengaging the decurler into the web will minimize or eliminate any changes in effect on the aim and other settings of the bowed roll.
Additional to the lead in roll, the decurler apparatus, as noted, can be provided with a lead out roll downstream of the decurler bar. The lead out roll may be made adjustable relative to the decurler bar. Preferably, the lead out roll is mounted so that at least one end can be adjusted, moved or raised or lowered in or out relative to the normal web path so as to incline or skew the lead out roll to stretch one or the other side or edge of the web more as is needed to overcome a xe2x80x9cloosexe2x80x9d web edge on one side or the other of the web. By varying the amount of bow, the relationship of the direction of the bow to the web, the amount the decurler bar or roll engages the web, and skewing or inclining adjustment of the downstream (lead out) roller, many adjustments and/or combinations can be had to overcome a less than ideal web curl profile, thus maintaining a consistent decurl across the web and resulting in flat or at least flatter sheets, particularly for webs with an uneven cross direction curl profile.
Further means are provided for maintaining the relative orientation of the decurler even though the mounting plates or arms of the carriage or frame for the decurler and lead in roll pivot. Yet further means are provided for controlling the movement of both sides of the mounting arms relative to the carriage so that they move together; that is so no undesired twist is induced into the apparatus.
The method and apparatus of the present invention can be used in any process or apparatus wherein a paper web will eventually be, at some subsequent time, either in that process or apparatus or another, in sheet form, such as in the paper converting field in a sheeter, or in a web press wherein the output is eventually made into sheets or press signatures.